Too many pupils in Sweden fail to achieve the syllabus goals in mathematics. Consequently different political initiatives have been introduced, including a recent reform that involves mandatory national examinations in mathematics for grade 3 pupils. However, a well functioning working memory capacity can be regarded as a crucial component for mathematical ability.The aim of this study was to examine the relationship between working memory capacity and mathematical performance measured by the national curriculum assessment in third-grade children (n=40). The national tests concerned six subareas within mathematics.The results showed that working memory could be deemed as a predictor for the overall mathematical ability. Thus, the significance of working memory contributions varied for the different mathematical domains assessed. We suggest that individual abilities such as working memory are important to take into consideration for the educational system with regard to learning. Cognitive implications for educational practice are discussed.